1. Field of the Invention
The present invention relates to a crosslinkable hot-melt adhesive coating based on a powder mixture comprising a commercially customary, amine-terminated copolyamide or copolyester and a pulverized extrudate consisting of an atactic polyolefin and a pulverulent isocyanate or an epoxide, for producing a base dot as a barrier to strikeback in double dot coating. The upper dot consists of an amine- or acid-regulated copolyamide, in order to ensure good attachment to the lower dot. The invention relates in particular to a hot-melt adhesive composition for the dot coating of bondable interlinings for the clothing industry, especially outerwear, and technical laminates. Instead of the copolyamide, it is also possible to employ HO-terminated copolyesters.
2. Description of the Background
In order to solve the problems regarding the reduced resistance to laundering and dry cleaning and regarding the relatively weak adhesion, improved hot-melt adhesive compositions, but also improved coating technologies, have been developed. Duodot or double dot coatings are described, for example, in patents DE 22 14 236, DE 22 31 723, DE 25 36 911 and DE 32 30 579.
Coating supports have been improved by using finer yarns with low-denier individual fibers down to the microfiber range and also synthetic yarns, examples being high-bulk acrylic or polyester yarns. The wovens originally used have largely been replaced by stitch-bonded fabrics. These new combinations lead to very soft, but also very open constructions which place even greater requirements on the coating methods and hot-melt adhesive compositions, especially with regard to strikeback and strikethrough of the hot-melt adhesive composition.
Costs and quality reasons have led to a marked reduction in the amount of coating applied per m.sup.2 on interlining material. Whereas formerly the amounts applied were commonly 18-25 g/m.sup.2, they are nowadays 7-15 g/m.sup.2.
Despite these small amounts, it is necessary to ensure sufficient adhesion and resistance properties for the hot-melt composition; in other words, the hot-melt adhesive must not strike away into the interlining, since then it would no longer be available for the actual bonding.
An object that had developed in the art was to find an effective strikeback barrier which exhibits high bond strength, good attachment of the upper dot to the base layer and good resistance to laundering and dry cleaning at reduced amounts of coating of the adhesive.
A range of strikeback barriers is known which are (i) crosslinking acrylate dispersions or polyurethane dispersions, to (ii) powder-filled pastes based on high-melting copolyamides or polyethylene to (iii) highly viscous thermoplastic polyurethane powders.
All systems have more or less severe disadvantages in terms of application, the attachment to the upper dot and/or resistance to laundering. In addition, the dispersions cannot be employed on coarse, hairy interlinings.
When self-crosslinking acrylate or polyurethane dispersions are coated on a fabric, partial crosslinking occurs, even in the course of coating, which leads to a deposit on the screens and thus to clogging of the stencil holes. Laborious cleaning of the unit is required. Great difficulties are experienced when there is production-induced standstill. A further problem is the attachment of the upper dot to the base layer. The highly viscous powder-filled systems based on polyamide, polyethylene and polyurethane do not achieve the required strikeback reliability.
It has so far not been possible to provide a stable crosslinkable system for the base dot. Either the isocyanates, which are employed preferably, can not be stabilized to water (the matrix for coating pastes), or the activation temperature for crosslinking (greater than 160.degree. C.) is too high.